I got a new Sterling Evoution 9.8 mm rope and decided to do some research on how they were made and what the strength ratings meant. Also found some good websites that describe impact forces and fall factors. Here's the link to the write-up:

Just a heads up, your linked post confuses impact force with the static strength of the rope.

I could see that being confusing. I tried to explain in the post that the weight (rope strength conversion area) was generated from a falling (dynamic) force that is not equal to the static weight (of the climber or object).

No, I don't think you get it. That's not a strength rating at all, dynamic or static. It's a resulting force from dropping a weight onto it. It's a measure of how "soft" a rope catches, and has NOTHING to do with strength.

The post still makes it seem like you don't know what impact force really means.

The UIAA fall test involves a 1.77 factor fall with an 80kg weight. The impact force rating is the maximum amount of force transferred through the rope (ie. to you) during the first test. UIAA standards require this force to be less than 12kN, and the rope must be able to go through at least 5 of these drops before the rope breaks.

A dynamic rope that stretches a lot usually has a lower impact force because it can stretch longer to absorb that impact. This would be desirable in a situation where the protection isn't that good, as it will lessen the load on the anchor/pro. A dynamic rope that doesn't stretch as much will usually have a higher impact force, but they also often last a little longer (more falls). This can be desirable for sport climbing where you're falling a lot on bomber protection. A static rope, on the other hand, barely stretches at all and will transfer a LOT of force onto a climber.

Dynamic ropes aren't tested with a static weight until they break because that's not how they're meant to be used. Static ropes are meant to be used with static weight, and they often have strength ratings in the 25-40kN range.

It's worth noting that only about 4.5kN of force on your abdomen is enough to suffer "serious" injuries (eg. 8-10% chance of death). An 8.8kN force would be VERY serious, likely putting your climbing career on hold for quite some time, and your rope could still do this 5 more times.

Also, dynamic lines dont actually have their tensile strength listed (or ultimate strength of the rope), which is why this part can be somewhat confusing.

In a real world scenario, ropes do not break. To my knowledge, a dynamic kernmantle line in good working condition has never broken in the field. They've been cut, there's been instances of corrosive materials destroying ropes, but a rope in good shape, no matter how severe the fall, has never broken to my knowledge.

So, the impact force becomes one of the numbers you care about- it tends to be a trade-off between a soft catch and durability. Most sport climbers will go for the lowest impact force possible, as a soft catch is wanted since they tend to fall alot more than the average trad climber. A trad climber, on the other hand, will often go for a rope that is known for its durability (and usually has a somewhat higher impact force).

All of that said, most single ropes land somewhere in the 8-9kn range for their impact force (as all ropes are made the same way for the most part). Beal can land below 8kn, and Maxim usually hits about 9kn, but thats about as much variance as you get. Ultimately, it doesnt matter as much as one might think it does.

Most sport climbers will go for the lowest impact force possible, as a soft catch is wanted since they tend to fall alot more than the average trad climber. A trad climber, on the other hand, will often go for a rope that is known for its durability (and usually has a somewhat higher impact force).

I've generally heard the opposite: trad climbers don't fall as often and when they do they're usually more "serious" falls and at the mercy of their protection, so they'll take a rope with a lower fall count in exchange for a lower impact force to minimize the risk of their protection from failing.

Sport climbers fall a lot, which favors durability, and the severity of their falls are usually very low: low fall factors, very dynamic belays (belayer usually not anchored into anything to restrict upwards pull like multi-pitch trad climbers do), and falling onto bomber gear (bolts) with little risk of it pulling. And of course, the less your rope stretches the less you'll have to climb back up when you fall!

Of course it's just personal preference though. I use the same rope for both sport and trad and haven't really given much thought about its ratings...

post updated, thanks for the heads up. I looked up the kN rating for gear and got it confused with carabiner strength ratings. I looked up the UIAA standards for rope and found a lot of useful information that helped me get the info correct.

I've generally heard the opposite: trad climbers don't fall as often and when they do they're usually more "serious" falls and at the mercy of their protection, so they'll take a rope with a lower fall count in exchange for a lower impact force to minimize the risk of their protection from failing.

Are you sure lower impact force = lower fall count? Many models of Beal ropes have very high fall count & lower impact force, but are notoriously non-durable. Sterling ropes, on the other hand, tend to have low fall count & middle of the road impact force but with durable sheathe (their 9.2 & 9.4 not-withstanding). Rope durability depends on use. Long trad routes tend to wear out the sheathe whereas frequent sport fall can result in core shot or rope stiffening too much for comfort (increased fall force).

Like Ian, I don't have separate ropes for sport and trad, even if perhaps this would be useful. Too expensive. Instead, like most climbers I know, I have my newer rope, which I will still lead on, and my older rope, which used to be my lead rope until it got too old/took too many falls/I could afford a new one. Now the older rope goes on toproping trips with the kids, and the one that used to be the older rope before that is a rug. So there is a pipeline for ropes in my house, just like the pipeline for us (school-work-social security-death).

Then there is my exception: a set of 8.1mm twin/half ropes I use mostly for alpine rock and ice. As bowshaa's blogpost notes, the cap for impact forces for ropes rated for twin/half use are lower, and each of the ropes in the pair are generally much "stretchier" than a single rope of similar length (and sometimes similar diameter, what with those new "skinny" 9.5ish redpointing ropes out now).

I am a big proponent of the twin rope system for alpine and ice, and one reason is the lower impact forces transferred to those less-than-optimal placements that are so often your only option on alpine terrain (bowshaa points out that impact forces are transferred to you/your internal organs on the end of your rope, but in a lead fall they are also transferred to your top placement, the item in your system that is suddenly being asked to become a lone toprope anchor...). In fact, the only truly big lead fall of my career was a 25 footer onto a stubby ice screw. My belayer gave me a good soft catch (which accounted for some of those 25 feet), but the twin ropes also stretched enough so the screw never budged and only the first row of stitching on the screamer pulled. Whew.

Are you sure lower impact force = lower fall count? Many models of Beal ropes have very high fall count & lower impact force, but are notoriously non-durable. Sterling ropes, on the other hand, tend to have low fall count & middle of the road impact force but with durable sheathe (their 9.2 & 9.4 not-withstanding). Rope durability depends on use. Long trad routes tend to wear out the sheathe whereas frequent sport fall can result in core shot or rope stiffening too much for comfort (increased fall force).

Generally, lower impact force results in lower durability.

The UIAA fall number is more or less a completely useless number to the consumer. New climbers tend to want ropes with higher numbers, thinking they are more durable, but this isnt directly true. Anyone who has climbed any length of time develops a taste for ropes and doesnt (or shouldnt) bother looking at this number.